1. Field of the Invention
The present invention relates to a bar code scanner using a laser beam for scanning a bar code to read code data.
2. Description of the Related Art
In many department stores and supermarkets, a POS (point-of-sales) system is introduced at present to efficiently manage merchandise and the checkout operation. This system employs a bar code reader provided with a bar code scanner, for scanning a bar code attached to an item by using a laser beam, detecting signal light scattered from the bar code by using a photodetector, and converting the detected signal light into an information form suitable for computational processing.
In general, the bar code reader is composed of a laser beam generating light source, a laser beam shaping optical system, a scanning optical system, a signal light detecting optical system, a waveform shaping circuit, and a bar code decoding circuit. A laser beam emerging from a He-Ne laser is shaped to have a suitable size by the laser beam shaping optical system, and a scanning pattern capable of universally reading a bar code is formed over a reading window by the scanning optical system. Then, the bar code is irradiated with this scanning pattern.
Scattered signal light reflected from the bar code is collected to the signal light detecting optical system, and is then converted into an electrical signal by a photodetector. The electrical signal is next shaped in the signal waveform shaping circuit, and is next decoded by the bar code decoding circuit. The decoded signal is next transmitted to a POS terminal. Although a recent bar code reader has been progressively reduced in size, the number of beams and the number of directions of beams forming a scanning beam pattern generated in the optical systems have not yet been increased. Accordingly, the reading performance of the scanner is maintained by setting to a given value or more the height of a bar code printed on or attached to an item and thereby increasing the probability that the beams pass across the bar code.
However, a smaller size of the bar code printed on or attached to the item can improve the image for the item. Further, in a supermarket dealing with a large amount of items, it is desired to register the items efficiently in a short time. One method for realizing this desire is to increase the number of scanning laser beams and/or the number of directions of the beams outgoing from the reading window, thereby allowing reading of the bar code irrespective of the size of the bar code, the passing position of the beams, and the angle of the bar code.
As a method of increasing the number of outgoing laser beams effective for reading of the bar code, there is known a method of increasing the rotational speed of a motor for driving a polygon mirror constituting the scanning optical system. In this method, however, it is necessary to increase the power of the motor, causing an increase in size of the motor or an increase in power consumption. Furthermore, the service life of the motor is also shortened. Thus, the above desire is difficult to realize according to this method.
As another method of increasing the number of outgoing beams, there is known a method of increasing the number of reflecting surfaces of the polygon mirror. However, the increase in number of reflecting surfaces of the polygon mirror results in a decrease in size of each reflecting surface and a decrease in scanning angle. As a result, the effective length of each scanning beam outgoing from the reading window becomes short. Further, in general, scanning pattern generation mirror means composed of a pluraliry of reflecting mirrors is provided to obtain a scanning pattern composed of scanning beams having many directions. In this case, the number of outgoing beams and the number of directions of the beams may be increased by a method of increasing the number of the mirrors constituting the scanning pattern generation mirror means. Also in this method, however, the effective length of each scanning beam outgoing from the reading window becomes short.